Most MMW antennas that operate at frequencies equal to or greater than 35 GHz use either a mechanical scanning approach or phase shifters for electronic steering. Phase shifters that operate at MMW frequencies are costly and introduce considerable RF losses. Mechanically steered antennas contain moving parts; are slow in response; and can be sensitive to shock and vibration. For this reason different beamforming antennas were investigated. Although most beamformers excel in one category, for example, greater scan range or bandwidth, only the Rotman lens offers a good compromise in performance for most categories. For example, see the following references: Y. T. Lo and S. W. Lee, Antenna Handbook: Theory, Appications and Design, Van Nostrand Reinhold Co., New York, N.Y., 1988; P. S. Hall and S. J. Vetterlein, Review of Radio Frequency Beamforming Techniques for Scanned and Multiple Beam Antennas, IEEE Proc., Vol. 137, Pt. H, No. 5, pp. 293-303, October 1990; and W. Rotman and R. F. Turner, Wide Angle Lens for Line Source Applications, IEEE Trans. Ant. Propogation. Vol. AP-11, pp. 623-632, November 1963.
In the past, Rotman lenses have been implemented with microstrip or stripline technology, which limits their use to between 6 and 18 GHz. The present invention enables the use of Rotman lenses at frequencies greater than approximately 18 GHz, especially in the millimeter wave region between 30 and 100 GHz.
Millimeter Wave (MMW) components are compact and well suited for integration into missile seeker heads, smart munitions, automobile collision avoidance systems, and synthetic vision systems. In these applications, low cost, rapid inertialess scanning of the antenna is desirable.